There have conventionally been known some aromatic polycarbodiimides obtained by polymerizing diphenylmethane diisocyanate (MDI) or tolylene diisocyanate (TDI) as a monomer. Such polycarbodiimides are used as a flame-retardant film or a heat-resistant adhesive because of its excellent heat resistance.
Although the polycarbodiimide film has a heat-resistance in the point that a volatile gas or decomposed monomer is not generated even if it is exposed to a high temperature of 400.degree. C. or more, if it has a low-moisture resistance or it is thermally treated at a temperature of 200.degree. C. or more, it will lose a self-supporting property and become brittle. As the result, the film cannot be practically used. Furthermore, the polymer has a low solubility in an organic solvent and has a low processability.